1. Field of the Invention
The present invention relates to a method for improving compatibility of a hearing aid with an antenna, and especially to a method that adds at least a metal frame near by a grounding surface of the antenna to lower the near-field quantity of an HAC (hearing aid compatibility) tested plane.
2. Description of the Prior Art
In using a hearing device (such as a hearing aid) for a wireless device, a user may hear a noise such as bi . . . , ng . . . or a long noise; some hearing devices has better ability in eliminating these interferences of noises, different wireless devices may have different amount of interference. When a digital mobile phone and a hearing aid are used simultaneously, an electric field may be induced near an antenna of the mobile phone, the pulse energy of its magnetic field may be absorbed by a microphone or a communication coil of the hearing aid and will be a sound of ghi . . . ghi . . . heard by a user of the hearing aid. American National Standards Institute (ANSI) established a specification of ANSI C63.19, FCC required that manufacturers of mobile phones and service providers of mobile phones must have more than 50% of their products satisfying the rules of limitation about the hearing aid EMI required by ANSI C63.19 since Feb. 18, 2008.
The standards of test of the rule specification about HAC (hearing aid compatibility) of ANSI C63.19 are as below:    a. a testing probe is used to measure electromagnetic field quantity of a plane of 5×5 cm2 which is 15 mm above a sound outlet of a mobile phone;    b. the tested plane is divided into 9 blocks, the maximum electromagnetic field strength of each block is taken;    c. the maximum electromagnetic strength of each of the blocks is used to define its class of HAC;    d. The differences between these classes of HAC are defined by a value of 5 dB, they are classes M1, M2, M3 and M4 (in which M3 and M4 meet the stipulated rule).
Thus for an antenna, we generally observe at the same time the HAC classes of their electric fields and magnetic fields, and take the worst class to define the HAC value of frequency spot.
The method of the present invention mainly is for lowering the strength of the electric field in a tested plane of an antenna, the strength can be lowered for about 3 dB, this can get an effective directly improvement for some antenna designs in critical states against the rule specification.